Process for stabilizing against decomposition halogenated hydrocarbons,and in particular chlorinated aliphatic hydrocarbons



United States Patent US. Cl. 260-6525 3 Claims ABSTRACT OF THE DISCLOSURE Liquid halogenated hydrocarbons (and particularly chlorinated aliphatic hydrocarbons such as trichloroethylene and perchloroethylene used as metal degreasing solvents, dry-cleaning solvents, and oiland fats-extraction solvents) are stabilized against decomposition by means of a stabilizing composition consisting essentially of stated small concentrations of the following four components: butylene oxide, di-isobutylene, thymol and dimethylbenzalhydrazone. A small quantity of an alkylhydrazine may also be present.

The present invention relates to the stabilization of halogenated hydrocarbons against decomposition. More particularly it relates to the stabilization against decomposition of chlorinated hydrocarbons, and especially chlorinated aliphatic hydrocarbons such as trichloroethylene and perchloroethylene, useful as solvents in various industrial processes.

It is well known that chlorinated hydrocarbons, and more particularly trichloroethylene and perchloroethylene, are widely used in various technical processes. These are especially useful as solvents for fats and other organic substances, for instance in degreasing processes for metals, in processes for the extraction of oils and fats, in the drycleaning of fabrics, etc.

Due to the action of heat, oxygen, light and water, these chlorinated hydrocarbons tend to decompose thereby forming acidic products such as hydrochloric acid, poisonous products such as phosgene, tarry substances etc., all of which cause serious troubles both during storage and transport as well as during their use and during the recovery operations of the solvent itself.

Furthermore, this decomposition is accelerated through the presence of metals or metal salts as Well as by the direct or indirect products of the decomposition itself, the decomposition thereby proceeding autocatalytically.

All of these drawbacks are particularly serious in the case of the degreasing of metals, and particularly the degreasing of metals containing iron or aluminum, wherein, owing to the severe operational conditions to which the solvent is subjected under the combined action, for more or less prolonged periods of time, of heat, of the oxygen, of moisture and of the metal itself, a considerable decomposition of the solvent takes place; a decomposition that in turn is accelerated by the chlorides which are formed by the action on the metal of the hydrochloric acid which is freed, thus causing serious corrosion phenomena on the metal pieces undergoing the degreas ing treatment.

It is therefore of fundamental practical importance in the industry to prevent the decomposition of these chlorinated solvents or to neutralize the damaging action of the decomposition products thereof.

For this purpose it is common technical practice to add to the chlorinated solvent suitable stabilizing agents. Many such stabilizing agents of various kinds have already been proposed for this purpose; in particular, there has been proposed the use of antioxidants, that is, compounds which inhibit the action of the air, or acid acceptors which have the function of neutralizing the acidity that gradually forms, thereby hindering the possibility of autocatalytic decomposition reactions.

The stabilizing system must furthermore be such as to ensure the neutrality of the solvent even under the most severe conditions (alkalinity of the solvent when imparted by stabilizers having a strong basic character is just as harmful as acidity, because such alkalinity makes the solvent quite unsuited for the degreasing of amphoteric metals such as aluminum and zinc) and furthermore the stabilizing system must exert a lasting stabilizing action both in the liquid phase as well as in the vapor phase customarily encountered during degreasing processes.

The necessity of the contemporaneous presence of all the above mentioned characteristics creates a situation by which the greatest part of the stabilizing agents so far suggested are definitely unsuited for an effective and lasting stabilization of chlorinated solvents.

Thus, the object of this invention is that of providing a new and efficient stabilizing agent for halogenated hydrocarbons, particularly suited for chlorinated solvents to be used in the degreasing of metals, which, besides exerting a sure and lasting anti-oxidizing action, that is, such as to ensure the inhibition of the formation of phosgene and hydrochloric acid, will also guarantee the neutrality of the solvent even under the most severe operational conditions.

It has now been discovered in accordance with the present invention that a stabilizing action of a sure and lasting effectiveness against the decomposition of halogenated hydrocarbons, and in particular of chlorinated hydrocarbons used as solvents in the degreasing of metals, is achieved by adding to the halogenated hydrocarbon solvent a stabilizing composition based on the combination of butylene oxide, di-isobutylene, thymol and dimethylbenzalhydrazone.

The above-mentioned composition may be used alone or in admixture with other stabilizers of previously known yp The quantity of stabilizing composition to be added to the halogenated hydrocarbon solvent depends on the type of solvent to be stabilized, on the expected use of the solvent, on the degree of stabilization desired, and on the possible presence of other additives.

In general, and for the most common applications, concentrations are preferably used varying from 0.1 to 0.4% by Weight of butylene oxide, from 0.01 to 0.1% by weight of di-isobutylene, from 0.001 to 0.02% by weight of thymol, and from 0.001 to 0.02% by weight of dimethylbenzalhydrazone. Although larger quantities of the several components may be used, they are not necessary.

Trichloroethylene and perchloroethylene stabilized according to the present invention do not show any tendency to decompose either during storage or during use under the most severe processing conditions such as in the degreasing of metals. Even after long heat-treatments trichloroethylene and perchloroethylene thus stabilized remain limpid and clear.

For certain applications it may furthermore be advantageous to use the stabilizing composition of this invention in combination with small quantities (for instance, 0.00050.002% by weight) of an alkyl-hydrazine, such as methyland ethyl-monoand symmetrical and/or asymmetrical di-hydrazines.

Besides trichloroethylene and perchloroethylene, various other halogenated hydrocarbons may be protected against decomposition by the stabilizing composition according to the present invention, such as chloroform, methylchloroform, methylene chloride, carbon tetrachloride, dichloroethylene, trichloroethane, vinylidene chloride, vinyl chloride, etc.

Further characteristics and advantages of the present invention are shown by the examples given in the accompanying Tables 1 and 2, showing non-stabilized trichloroethylene and perchloroethylene samples and samples of trichloroethylene and perchloroethylene stabilized by the stabilizing composition of the present invention. The compositions there ShOWn have been evaluated for the purposes of their stability" characteristics on the basis of the In such a stability test 200 ml. of trichloroethylene or of perchloroethylene are reflux-boiled in a flask of 500 ml. capacity for 48 hours, once alone by itself and a second time in admixture with the reported quantities of the several constituents of the stabilizing composition, while bubbling oxygen saturated with water through it by means of a glass tube 3 mm. in diameter, at a rate of 10-12 bubbles per minute. A small steel plate of x 2 x A inch is suspended in the vapor phase while in the liquid phase a small steel plate of 4 x x inch is introduced. As a light and heat source a sanded 150 watt lamp is placed under the flask.

At the end of the test one determines the acidity of the trichloroethylene or of the perchloroethylene, the pH on the aqueous extracts, using in all cases the same Water/trichloroethylene or perchloroethylene ratio (1:1), and then one observes the aspect of the small steel test plates and of the trichloroethylene or of the perchloroethylene themselves.

The results of the tests are recorded in the accompanying Tables 1 and 2, where the percentages of the difierent additives are given in percentages by weight with respect to the trichloroethylene or to the perchloroethylene.

The above tests clearly show the elfectiveness of the stabilization of trichloroethylene and perchloroethylene according to the present invention. In fact the pH remains neutral, phosgene is completely absent, and the aspect of the small steel test plates and of the trichloroethylene or of the perchloroethylene is fully satisfactory even after the severe conditions of the cited oxidation test.

What is claimed is: 1. A liquid chlorinated hydrocarbon stabilized against decomposition, comprising trichloroethylene or perchloroethylene in admixture with a stabilizing composition consisting essentially of butylene oxide, di-isobutylene, thymol and dimethylbenzalhydrazone in quantities varying, respectively, from about 0.1 to 0.4% by Weight, from about 0.01 to 0.1% by weight, from about 0.001 to 0.02% by weight, and from about 0.001 to 0.02% by weight.

2. Trichloroethylene stabilized against decomposition, comprising trichloroethylene in admixture with a stabilizing composition consisting essentially of butylene oxide, di-isobutylene, thymol and dimethylbenzalhydrazone in quantities varying, respectively, from about 0.1 to 0.4% by weight, from about 0.01 to 0.1% by weight, from about 0.001 to 0.02% by weight, and from about 0.001 to 0.02% by weight.

3. Perchloroethylene stabilized against decomposition, comprising perchloroethylene in admixture with a stabilizing composition consisting essentially of from about 0.1 to 0.4% by weight of butylene oxide, of from about 0.01 to 0.1% by weight of di-isobutylene, of from about 0.001 to 0.02% by weight of thyme], and of from about 0.001 to 0.02% by weight of dimethylbenzalhydrazone.

TABLE 1 pH of the pH of the aqueous aqueous extract extract before after Color of the Aspect of the Example the oxidathe oxidatriehlorosmall steel plate No. Stabilizer tion test tion test Phosgene ethylene in vapor phase 1 None (comparison) 7 1 SatI-d Yellow Highly corroded,

m e 2 Butylene oxide 0.25%; di-isobutylene 0.03%; thymol 7 7 Absent Limpid, Perfectly bright 0.005%; dimethylbenzalhydrazone 0.005%. colorless. and absolutely uncorroded.

TABLE 2 pH of the pH of the aqueous exaqueous ex- Hydrotract before tract after chloric Color of the Aspect of the Example I the oxidathe oxldaacidity, perchlorosmall steel plate No. Stabilizer tion test tion test Phosgene percent ethylene in vapour phase 1 None (comparison) 7 1.2 *3 Yellow Opaque. 2 Butylene oxide 0.25%; di-isobutylene 0.03%; thymul 7 6.5 Absent... 0.0001 Colourless... Perfectly bright.

0.005%; dimethylbenzal-hydrazone 0.005%.

* Inclusive of phosgene calculated as HCl.

1/1969 Patron et al 260-6525 FOREIGN PATENTS 684,156 12/1966 Belgium 260-6525 HOWARD T. MARS, Primary Examiner US. Cl. X.R. 

